This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The overall objective of this study is to use gene expression analysis to determine the profile of host genes that are differentially expressed after SIV infection in a natural host that does not develop AIDS, as compared to a non-natural host that progresses to AIDS. Peripheral lymph node biopsy tissues before and two weeks after SIVsmE041 infection in four sooty mangabeys and four rhesus macaques are being subjected to microarray analysis. Early differences in host gene expression in response to SIV in the two species should provide valuable insight into mechanisms of protection against AIDS in natural hosts.